Trifluoromethyl analogs of X-ray contrast media for magnetic resonance imaging

ABSTRACT

Methods and compositions are disclosed for enhancing  19  F magnetic resonance imaging which utilize trifluoromethyl derivatives of iodinated X-ray contrast media. Typical magnetic resonance contrast media within the scope of the present invention include bis(trifluoromethyl)benzene derivatives, tris(trifluoromethyl)benzene derivatives, tetrakis(trifluoromethyl)benzene derivatives, and other related trifluoromethylated benzene derivatives.

This is a divisional of U.S. application Ser. No. 07/782,153 filed Oct.25, 1991 now U.S. Pat. No. 5,318,770.

BACKGROUND OF THE INVENTION

This invention relates to compositions for improving magnetic resonanceimaging ("MRI"), magnetic resonance spectroscopy ("MRS"), and magneticresonance spectroscopy imaging ("MRSI"). More particularly, the presentinvention relates to low concentration fluorine-19 imaging agents.

The technique of MRI encompasses the detection of certain atomic nuclei(those possessing magnetic dipole moments) utilizing magnetic fields andradio-frequency radiation. It is similar in some respects to X-raycomputed tomography ("CT") in providing a cross-sectional display of thebody organ anatomy with excellent resolution of soft tissue detail. Thetechnique of MRI is advantageously non-invasive as it avoids the use ofionizing radiation.

The hydrogen atom, having a nucleus consisting of a single unpairedproton, has the strongest magnetic dipole moment of any nucleus. Sincehydrogen occurs in both water and lipids, it is abundant in the humanbody. Therefore, MRI is most commonly used to produce images based uponthe distribution density of protons and/or the relaxation times ofprotons in organs and tissues. Other nuclei having a net magnetic dipolemoment also exhibit a nuclear magnetic resonance phenomenon which may beused in MRI, MRS, and MRSI applications. Such nuclei include carbon-13(six protons and seven neutrons), fluorine-19 (9 protons and 10neutrons), sodium-23 (11 protons and 12 neutrons), and phosphorus-31 (15protons and 16 neutrons).

While the phenomenon of MRI was discovered in 1945, it is onlyrelatively recently that it has found application as a means of mappingthe internal structure of the body as a result of the originalsuggestion of Lauterbur (Nature, 242, 190-191 (1973)). The fundamentallack of any known hazard associated with the level of the magnetic andradio-frequency fields that are employed renders it possible to makerepeated scans on vulnerable individuals. Additionally, any scan planecan readily be selected, including transverse, coronal, and sagittalsections.

In an MRI experiment, the nuclei under study in a sample (e.g. protons,¹⁹ F etc.) are irradiated with the appropriate radio-frequency (RF)energy in a controlled gradient magnetic field. These nuclei, as theyrelax, subsequently emit RF energy at a sharp resonance frequency. Theresonance frequency of the nuclei depends on the applied magnetic field.

According to known principles, nuclei with appropriate spin when placedin an applied magnetic field (B, expressed generally in units of gaussor Tesla (10⁴ gauss)) align in the direction of the field. In the caseof protons, these nuclei precess at a frequency, F, of 42.6 MHz at afield strength of 1 Tesla. At this frequency, an RF pulse of radiationwill excite the nuclei and can be considered to tip the netmagnetization out of the field direction, the extent of this rotationbeing determined by the pulse, duration and energy. After the RF pulse,the nuclei "relax" or return to equilibrium with the magnetic field,emitting radiation at the resonant frequency. The decay of the emittedradiation is characterized by two relaxation times, T₁ and T₂. T₁ is thespin-lattice relaxation time or longitudinal relaxation time, that is,the time taken by the nuclei to return to equilibrium along thedirection of the externally applied magnetic field. T₂ is the spin-spinrelaxation time associated with the dephasing of the initially coherentprecession of individual proton spins. These relaxation times have beenestablished for various fluids, organs, and tissues in different speciesof mammals.

For protons and other suitable nuclei, the relaxation times T₁ and T₂are influenced by the environment of the nuclei (e.g., viscosity,temperature, and the like). These two relaxation phenomena areessentially mechanisms whereby the initially imparted radio-frequencyenergy is dissipated to the surrounding environment. The rate of thisenergy loss or relaxation can be influenced by certain molecules orother nuclei which are paramagnetic. Chemical compounds incorporatingthese paramagnetic molecules or nuclei may substantially alter the T₁and T₂ values for nearby nuclei having a magnetic dipole moment. Theextent of the paramagnetic effect of the given chemical compound is afunction of the environment within which it finds itself.

In MRI, scanning planes and sliced thicknesses can be selected. Thisselection permits high quality transverse, coronal and sagittal imagesto be obtained directly. The absence of any moving parts in MRIequipment promotes a high reliability. It is believed that MRI has agreater potential than CT for the selective examination of tissuecharacteristics. The reason for this being that in CT, X-ray attenuationand coefficients alone determine image contrast, whereas at least fourseparate variables (T₁, T₂, proton density, and flow) may contribute tothe MRI signal. For example, it has been shown (Damadian, Science, 171,1151 (1971)) that the values of the T₁ and T₂ relaxation in tissues aregenerally longer by about a factor of two (2) in excised specimens ofneoplastic tissue compared with the host tissue.

By reason of its sensitivity to subtle physiochemical differencesbetween organs and/or tissues, it is believed that MRI may be capable ofdifferentiating different tissue types and in detecting diseases whichinduce physicochemical changes that may not be detected by X-ray or CTwhich are only sensitive to differences in the electron density oftissue.

In some cases, the concentration of nuclei to be measured is notsufficiently high to produce a detectable MR signal. For instance, since¹⁹ F is present in the body in very low concentration, a fluorine sourcemust be administered to a subject to obtain a measurable ¹⁹ F MR signal.Signal sensitivity is improved by administering higher concentrations offluorine or by coupling the fluorine to a suitable "probe" which willconcentrate in the body tissues of interest. High fluorine concentrationmust be balanced against increased tissue toxicity. It is also currentlybelieved that a fluorine agent should preferably contain magneticallyequivalent fluorine atoms in order to obtain a clear, strong signal.

From the foregoing, it would be a significant advancement in the art toprovide fluorine MRI agents for enhancing images of body organs andtissues which may be administered in relatively low concentrations, yetprovide a clear, strong signal.

Such MRI agent are disclosed and claimed herein.

SUMMARY OF THE INVENTION

The present invention provides methods and compositions for improvedmagnetic resonance imaging and spectroscopy, including fluorine-19 MRIagents. The MRI agents are derived from the class iodinated X-raycontrast media ("XRCM"). Over the years, a number of triiodinatedbenzene derivatives have been developed and brought to market as XRCM.The XRCM that have been brought successfully to market have had very lowtoxicity because of the large doses required for X-ray imaging.

Since the doses required for proton magnetic resonance imaging areconsiderably lower than XRCM doses, magnetic resonance contrast media("MRCM") which are structurally similar to XRCM should result in aproduct having a high safety index (the ratio of toxic dose to imagingdose). Even if the MRCM is ¹⁹ F based, the doses should be less thanthat for XRCM such that the resulting ¹⁹ F MRCM has a high safety index.

The present invention takes advantage of the low toxicity oftriiodinated benzyl XRCM by replacing the iodine with trifluoromethyl("CF₃ ") groups or groups containing CF₃. Typical CF₃ analogs of XRCMwithin the scope of the present invention includebis(trifluoromethyl)benzene derivatives, tris(trifluoromethyl)benzenederivatives, tetrakis(trifluoromethyl)benzene derivatives, and otherrelated trifluoromethylated benzene derivatives.

Both iodine and CF₃ are similar in size. Therefore, CF₃ replacement ofiodine does not introduce steric effects that would affect chemical andbiological stability. Moreover, the CF₃ groups are chemically andbiologically inert like iodine. The CF₃ substituted MRCM within thescope of the present invention may be prepared such that all thefluorines are substantially chemically equivalent to avoid imagingproblems associated with non-equivalent nuclei.

Preparation of CF₃ substituted MRCM with 2-4 CF₃ groups would have 6-12fluorines per molecule, thereby improving the efficacy of the moleculeand lowering the imaging dose and raising the safety index.

Also disclosed are diagnostic compositions and methods of performing MRdiagnostic procedures which involve administering to a warm-bloodedanimal a diagnostically effective amount of the above-described fluorinesubstituted MRCM compositions and then exposing the warm-blooded animalto a MR procedure.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides novel fluorine MRCM. The MRCM of thepresent invention are trifluoromethyl derivatives of XRCM. For example,a number of triiodo benzene XRCM are modified within the scope of thepresent invention by replacing iodine with CF₃ groups or with CF₃substituted nitroxide radicals. Typical trifluoromethyl XRCM derivativeswithin the scope of the present invention include (a)bis(trifluoromethyl)benzene derivatives, (b)tris(trifluoromethyl)benzene derivatives, (c)tetrakis(trifluoromethyl)benzene derivatives, and (d) other relatedtrifluoromethylated benzene derivatives. Generic structures for thesetrifluoromethyl MRCM compounds follows:

(a) bis(trifluoromethyl)benzene derivatives: ##STR1## where X may be:--CONR₁ R₂, --NR₁ COR₂, --SO₂ NR₁ R₂, --CO₂ H, and pharmaceuticallyacceptable salts thereof, and where R₁ and R₂ may be same or differentand are from the group: H, alkyl, and hydroxyalkyl, but usually at leastone is hydroxyalkyl. The following is an example of abis(trifluoromethyl)benzene derivative within the scope of the presentinvention: ##STR2## where X₁, X₂, and X₃ may be: --H, --CONR₁ R₂, --NR₁COR₂, --SO₂ NR₁ R₂, --CO₂ H, and pharmaceutically acceptable saltsthereof, and where R₁ and R₂ may be same or different and are from thegroup: H, alkyl, and hydroxyalkyl, but usually at least one ishydroxyalkyl. The following are examples of tris(trifluoromethyl)benzenederivatives within the scope of the present invention: ##STR3## where X₁and X₂ may be: --CONR₁ R₂, --NR₁ COR₂, --SO₂ NR₁ R₂, --CO₂ H, andpharmaceutically acceptable salts thereof, and where R₁ and R₂ may besame or different and are from the group: H, alkyl, and hydroxyalkyl,but usually at least one is hydroxyalkyl. The following is an example ofa tetrakis(trifluoromethyl)benzene derivative within the scope of thepresent invention: ##STR4## where X may be: --CONR₁ R₂, --NR₁ COR₂,--SO₂ NR₁ R₂, --CO₂ H, and pharmaceutically acceptable salts thereof,and where R₁ and R₂ may be same or different and are from the group: H,alkyl, and hydroxyalkyl, but usually at least one is hydroxyalkyl, andwhere n=1-5 and m=6-n.

The CF₃ substituted MRCM within the scope of the present invention arepreferably prepared such that all the fluorines are substantiallychemically equivalent to avoid imaging problems associated withnon-equivalent nuclei. In addition, the CF₃ substituted MRCM may beprepared with a large number of fluorine atoms per molecule, therebyimproving the efficacy of the molecule and lowering the imaging dose.

The ¹⁹ F MRCM compounds of this invention are preferably formulated intodiagnostic compositions for enteral or parenteral administration. TheMRCM formulations may contain conventional pharmaceutical carriers andexcipients appropriate for the type of administration contemplated.

For example, parenteral formulations for ¹⁹ F imaging advantageouslycontain a sterile aqueous solution or suspension of a trifluoromethylMRCM according to this invention. Various techniques for preparingsuitable pharmaceutical solutions and suspensions are known in the art.Such solutions also may contain pharmaceutically acceptable buffers,stabilizers, antioxidants, and electrolytes, such as sodium chloride.Parenteral compositions may be injected directly or mixed with a largevolume parenteral composition for systemic administration.

Formulations for enteral administration may vary widely, as iswell-known in the art. In general, such formulations include adiagnostically effective amount of a ¹⁹ F MRCM in an aqueous solution orsuspension. Such enteral compositions may optionally include buffers,surfactants, adjuvants, thixotropic agents, and the like. Compositionsfor oral administration may also contain flavoring agents and otheringredients for enhancing their organoleptic qualities.

The diagnostic compositions within the scope of the present inventionare administered in doses effective to achieve the desired enhancementof the NMR image. Such doses may vary widely, depending upon the degreeof fluorination, the organs or tissues which are the subject of theimaging procedure, the NMR imaging equipment being used, etc. Typicaldoses of the diagnostic compositions are in the range from about 0.005to about 20 mmol/kg body weight, and preferably in the range from about0.05 to about 5 mmol/kg body weight.

It has been found that the addition of paramagnetic species to thediagnostic compositions greatly improves the relaxation properties of ¹⁹F and the resulting ¹⁹ F image. The paramagnetic species may beadministered in doses from about 1 μmol/kg body weight to about 2mmol/kg body weight, and preferably in doses from about 50 μmol/kg toabout 0.5 mmol/kg body weight. Typical paramagnetic species include wellknown complexes of paramagnetic metal ions.

In general, complexes of paramagnetic metal ions of elements with anatomic number of 21 to 29, 42 to 44, and 58 to 70 may improve therelaxivity of ¹⁹ F. Suitable such ions include chromium(III),manganese(II), manganese(III), iron(II), iron(III), cobalt(II),nickel(II), copper(II), praseodymium(III), neodymium(III), samarium(III)and ytterbium(III). Because of their very strong magnetic moments,gadolinium(III), terbium(III), dysprosium(III), holmium(III) anderbium(III) are preferred.

The diagnostic compositions of this invention are used in a conventionalmanner in magnetic resonance procedures. Compositions may beadministered in a sufficient amount to provide adequate visualization,to a warm-blooded animal either systemically or locally to an organ ortissues to be imaged, and the animal then subjected to the MRIprocedure. The compositions enhance the magnetic resonance imagesobtained by these procedures.

The following examples are offered to further illustrate the presentinvention. These examples are intended to be purely exemplary and shouldnot be viewed as a limitation on any claimed embodiment.

Example 1 Synthesis ofN-(2,3-dihydroxypropyl)-3,5-bis(trifluoromethyl)-benzenecarboxamide

N-(2,3-dihydroxypropyl)-3,5-bis(trifluoromethyl)benzenecarboxamide, abis(trifluoromethyl)benzene derivative, is prepared by dissolving 4.2 g(50 mmol) sodium bicarbonate and 4.6 g (50 mmol) 3-amino-1,2-propanediolin 50 mL of water. A solution of 3,5-bis(trifluoromethyl) benzoylchloride (13.8 g, 50 mmol) in 50 mL of toluene is added. Theheterogeneous mixture is stirred for 18 hours at room temperature. Themixture is poured into a separatory funnel. The aqueous layer isseparated, washed with ether and evaporated. The residue is purified byC₁₈ chromatography to give the amide,N-(2,3-dihydroxypropyl)-3,5-bis(trifluoromethyl)benzenecarboxamide. Thechemical reaction is shown below: ##STR5##

Example 2 Synthesis ofN,N'-bis(2,3-dihydroxypropyl)-5-[(hydroxyacetyl)-(2-hydroxyethyl)-amino]-2,4,6-tris(trifluoromethyl)-1,3-benzenedicarboxamide

N,N'-bis(2,3-dihydroxypropyl)-5-[(hydroxyacetyl)-(2-hydroxyethyl)-amino]-2,4,6-tris(trifluoromethyl)-1,3benzenedicarboxamide,a tris(trifluoromethyl)benzene derivative, is prepared as follows: amixture ofN,N'-bis(2,3-dihydroxypropyl)-5[(hydroxyacetyl)-(2-hydroxyethyl)-amino]-2,4,6-triiodo-1,3-benzenedicarboxamide(20 g, 25 mmol), sodium trifluoroacetate (61.2 g, 450 mmol), andcopper(I) iodide (42.8 g, 225 mmol) in 500 mL of N,N-dimethylacetamideis refluxed under argon for six hours. The solvent is evaporated. Theproduct is isolated from the crude residue by C₁₈ chromatography. Thechemical reaction is shown below: ##STR6##

Example 3 Synthesis of 3,5-Bis(acetylamino)-2,4-6-tris(trifluoromethyl)benzenecarboxylic acid, meglumine salt

3,5-Bis(acetylamino)-2,4-6-tris(trifluoromethyl) benzenecarboxylic acid,a tris(trifluoromethyl)benzene derivative, is prepared according to theprocedure of Example 2, except that 3,5-Bis(acetylamino)-2,4-6-triiodobenzenecarboxylic acid is used instead ofN,N'-bis(2,3-dihydroxypropyl)-5[(hydroxyacetyl)-(2-hydroxyethyl)-amino]-2,4,6-triiodo-1,3-benzenedicarboxamide.The chemical reaction is shown below: ##STR7##

Example 4 Synthesis of2,3,5,6-tetrakis(trifluoromethyl)-1,4-benzenedicarboxylic acid,dimeglumine salt

2,3,5,6-tetrakis(trifluoromethyl)-1,4-benzenedicarboxylic acid isprepared by charging a one liter stainless-steel autoclave with1,2,4,5benzenetetracarboxylic acid (51 g, 200mmol) then cooled in liquidnitrogen. Hydrogen fluoride (100 g, 5.0 mol) and sulfur tetrafluoride(173 g, 1.6 mol) are added. The autoclave is sealed and heated at 150°C. for six hours. The gases are vented and the contents are poured ontoice. The mixture is transferred to a separatory funnel and extractedinto ether. The ether layers are washed with dilute sodium hydroxide,dried over magnesium sulfate, filtered and evaporated to leave crudeproduct. Recrystallization is used to give pure1,2,4,5-tetrakis(trifluoromethyl)benzene. The chemical reaction is shownbelow: ##STR8##

A solution of n-butyl lithium (6.4 g, 100 mmol) in hexanes is added atroom temperature to a solution of1,2,4,5-tetrakis(trifluoromethyl)benzene (16.9 g, 50 mmol) 200 mL ofanhydrous ether under argon. After one hour the reaction mixture ispoured onto dry ice. The mixture is taken up into water, washed withether and acidified to pH 2. The product is extracted into ether, washedwith water and brine, dried over magnesium sulfate, filtered andevaporated. The crude product is recrystallized. The dimeglumine salt isprepared by adding two equivalents of N-methyl-D-Glucamine inappropriate solvent. ##STR9##

From the foregoing, it will be appreciated that the present inventionprovides fluorine MRI agents for enhancing images of body organs andtissues which may be administered in relatively low concentrations, yetprovide a clear, strong signal.

The invention may be embodied in other specific forms without departingfrom its spirit or essential characteristics. The described embodimentsare to be considered in all respects only as illustrative and notrestrictive. The scope of the invention is, therefore, indicated by theappended claims rather than by the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

What is claimed is:
 1. A method for obtaining fluorine-19 magnetic resonance images of body organs and tissues which comprises:(a) administering to a mammal having organs and tissues, a diagnostically effective amount of a trifluoromethylbenzene derivative and paramagnetic species in a pharmaceutically acceptable carrier, said trifluoromethyl benzene derivative having a general formula: ##STR10## where X is --CONR₁ R₂, --NR₁ COR₂, --SO₂ NR₁ R₂, --CO₂ H, or pharmaceutically acceptable salts thereof, and where R₁ and R₂ may be same or different and are selected from the group consisting of H, alkyl, and hydroxyalkyl, and where n is in the range from 1 to 5 and m=6-n; and (b) imaging the organs and tissues.
 2. A method for obtaining fluorine-19 magnetic resonance images of body organs and tissues which comprises:(a) administering to a mammal having organs and tissues, a diagnostically effective amount of a trifluoromethylbenzene derivative and paramagnetic species in a pharmaceutically acceptable carrier, said trifluoromethyl benzene derivative having a general formula: ##STR11## where X is --CONR₁ R₂, --NR₁ COR₂, --SO₂ NR₁ R₂, --CO₂ H, or pharmaceutically acceptable salts thereof, and where R₁ and R₂ may be same or different and are selected from the group consisting of H, alkyl, and hydroxyalkyl; and (b) imaging the organs and tissues.
 3. A method for obtaining fluorine-19 magnetic resonance images as defined in claim 2, wherein the trifluoromethylbenzene derivative includes: ##STR12##
 4. A method for obtaining fluorine-19 magnetic resonance images of body organs and tissues which comprises:(a) administering to a mammal having organs and tissues, a diagnostically effective amount of a trifluoromethylbenzene derivative in a pharmaceutically acceptable carrier, said trifluoromethyl benzene derivative paramagnetic species having a general formula: ##STR13## where X₁, X₂, and X₃ are --H, --CONR₁ R₂, --NR₁ COR₂, --SO₂ NR₁ R₂, --CO₂ H, or pharmaceutically acceptable salts thereof, and where R₁ and R₂ may be same or different and are selected from the group consisting of H, alkyl, and hydroxyalkyl; and (b) imaging the organs and tissues.
 5. A method for obtaining fluorine-19 magnetic resonance images as defined in claim 4 wherein the trifluoromethylbenzene derivative includes: ##STR14##
 6. A method for obtaining fluorine-19 magnetic resonance images as defined in claim 4, wherein the trifluoromethylbenzene derivative includes: ##STR15##
 7. A method for obtaining fluorine-19 magnetic resonance images of body organs and tissues which comprises:(a) administering to a mammal having organs and tissues, a diagnostically effective amount of a trifluoromethylbenzene derivative and paramagnetic species in a pharmaceutically acceptable carrier, said trifluoromethyl benzene derivative having a general formula: ##STR16## where X₁ and X₂ are --H, --CONR₁ R₂, --NR₁ COR₂, --SO₂ NR₁ R₂, --CO₂ H, or pharmaceutically acceptable salts thereof, and where R₁ and R₂ may be same or different and are selected from the group consisting of H, alkyl, and hydroxyalkyl; and (b) imaging the organs and tissues.
 8. A diagnostic composition suitable for enteral or parenteral administration to a warm-blooded animal comprising:a diagnostically effective amount of a trifluoromethylbenzene derivative and paramagnetic species, said derivative having a general formula: ##STR17## where X₁, X₂, and X₃ are --H, --CONR₁ R₂, --NR₁ COR₂, --SO₂ NR₁ R₂, --CO₂ H, or pharmaceutically acceptable salts thereof, and where R₁ and R₂ may be same or different and are selected from the group consisting of H, alkyl, and hydroxyalkyl; and a pharmaceutically acceptable carrier.
 9. A diagnostic composition suitable for enteral or parenteral administration to a warm-blooded animal comprising:a diagnostically effective amount of a trifluoromethylbenzene derivative and paramagnetic species, said derivative having a general formula: ##STR18## where X₁ and X₂ are --H, --CONR₁ R₂, --NR₁ COR₂, --SO₂ NR₁ R₂, --CO₂ H, or pharmaceutically acceptable salts thereof, and where R₁ and R₂ may be same or different and are selected from the group consisting of H, alkyl, and hydroxyalkyl; and a pharmaceutically acceptable carrier. 